The research proposed will attempt to improve clinical application of selected aspects of cardiac electrophysiology. Methods will include observations on patients, animal experimentation and computer modeling. Extensive sampling of body or cardiac surface potentials is one of the major means proposed to achieve improved applications of electrophysiology and would be used in several projects. These projects have been separated on the basis of objectives which include a) correlation of body surface potentials with independent evidence of disease, b) estimation of myocardial infarct size, c) detection of states at high risk of arrhythmias, d) development of quantitative analytic methods for data compression and interpretation of extensive ECG examinations, 3) development of a self-contained mapping system and f) determination of activation sequence in ischemic tissue. Other areas of emphasis in the program are neural effects on cardiac electrophysiology, experimental studies and computer modeling of cardiac arrhythmias and studies of ventricular repolarization and the ST-T deflection of the ECG.